Coating compound, a process for its preparation and its use for the production of coatings

ABSTRACT

An aqueous two-component coating agent whose binder consists essentially of a combination of a) a polyol component present dissolved and/or dispersed in water comprising a1) at least one water-dilutable polymerisation resin or polycondensation resin with a molecular weight Mn of over 500 possessing hydroxyl groups and a2) a reactive diluent consisting of at least one water-soluble compound with a molecular weight Mn of under 500 capable of reacting with isocyanate groups and b) a polyisocyanate component with a viscosity at 23° C. of from 50 to 10 000 mPa present emulsified in the aqueous solution or dispersion, a method for producing such coating agents wherein the said polyisocyanate component is emulsified in the said aqueous solution or dispersion with the optional incorporation of auxiliary substances and additives in the system prior to adding the polyisocyanate, and the use of the coating agents for the production of air-drying and/or heat-drying coatings.

The present invention relates to a novel aqueous coating agent based ona polyol component present dissolved and/or dispersed in water,consisting of one high-molecular polymerization resin orpolycondensation resin and a reactive diluent and a polyisocyanatecomponent present emulsified in it, a method for producing such coatingagents and their use for the production of coatings.

Aqueous lacquer systems are gaining increasingly in importance oneconomic and ecological grounds. The replacement of conventional lacquersystems is however proceeding more slowly than was initially expected.

There are numerous reasons for this. Thus aqueous dispersions frequentlystill have disadvantages with regard to processing when compared withlacquer systems dissolved in organic solvents. In aqueous solutions,however, there is the problem of adequate solubility in water on the onehand as well as the opposite effect derived from it of lower waterresistance of the coatings compared with conventionally dissolvedlacquer systems. Added to this there are processing problems which inmany cases result from the high viscosity and anomalies of viscosity andwhich hitherto have been surmounted by using organic solubilisingagents. The quantity of solubilising agent that can be used for this islimited, as otherwise the ecological purpose of aqueous systems isdefeated.

For this reason there were used in melamine resin cross-linked bindersystems reactive diluents that were already water-dilutable (U.S. Pat.Nos. 4,031,052, 4,171,294, 4,276,210 or DE-OS 2,446,760 or 2,847,532)which on one hand favourably influence the solubility of the polymersystems but on the other hand became incorporated into the coatingsthrough melamine resin cross-linking. However the reactivity of manyaqueous melamine resins is so low that in many cases the cross-linkingtemperatures required are so high that the reactive diluents can escapefrom the coatings prior to cross-linking.

Quite recently aqueous two-component polyurethane systems have becomeknown (DE-OS 3,829,587) with a binder consisting of a polyacrylic resinpresent dissolved and/or dispersed in water combined with apolyisocyanate with free isocyanate groups present emulsified in thisdispersion or solution. Here it concerns essentially solvent-freesystems, which is already evident from the fact that the solvents whichwere used in the preparation of the polymer resins are removed prior toproducing the aqueous preparation. The concomitant use of reactivediluents is not discussed in the reference cited above.

Surprisingly it was then found that the use of reactive diluents, i.e.of low-molecular, not easily volatilised, liquid compounds with groupscapable of reacting with isocyanate groups of the kind described in moredetail below in aqueous two-component polyurethane systems based onhigh-molecular polymerization resins or polycondensation resinspossessing hydroxyl groups and polyisocyanates, with free isocyanategroups result in a considerable improvement in systems as regards thedilutability in water of the components of the binder and the propertiesof the lacquer coatings produced from the binding agents. Theseadvantages need not be acquired at the expense of the ecologicaldisadvantage of usual solvents, as the non-volatile reactive diluentsare incorporated in the lacquer film when the coating agent isprocessed.

The present invention provides coating agents, whose binder consistsessentially of a combination of

a) a polyol Component present dissolved and/or dispersed in water and

b) a polyisocyanate component with a viscosity at 23° C. of from 50 to10,000 mPa.s present emulsified in the aqueous solution and/ordispersion of the polyol component a)

in quantities corresponding to an equivalent proportion of isocyanategroups of component b) to active hydrogen atoms of component a) of from0.5: 1 to 5: 1, characterised in that component a) consists essentiallyof a combination of

a1) a high-molecular polyol component consisting essentially of at leastone water-dilutable polymerization resin or polycondensation resin witha molecular weight Mn of over 500 possessing hydroxyl groups with

a2) 5 to 70% by weight, related to the weight of component a1), of areactive diluent consisting of at least one water-soluble compound thatis not distillable at normal pressure or that has a boiling point of atleast 150° C. with a molecular weight Mn of under 500 and having atleast one group capable of reacting with isocyanate groups.

The present invention also provides a method for producing such coatingagents, characterised in that a polyisocyanate component b) with aviscosity at 23° C. of from 50 to 10,000 mPa.s consisting of at leastone organic polyisocyanate is emulsified in an aqueous solution ordispersion of a high-molecular polyol component a1) consistingessentially of at least one water-dilutable polymerization resin orpolycondensation resin with a molecular weight Mn of over 500 possessinghydroxyl groups which contains 5 to 70% by weight, related to the weightof component a1), of a reactive diluent a2) consisting of at least onewater-soluble compound that is not distillable at normal pressure orthat has a boiling point of at least 150° C. with a molecular weight Mnof under 500 and having at least one group capable of reacting withisocyanate groups, wherein the quantitative proportions of theindividual components correspond to an equivalent proportion ofisocyanate groups to groups capable of reacting with isocyanate groupsof from 0.5: 1 to 5: 1, and wherein optionally concomitantly usedauxiliary substances and additives are incorporated in the system priorto addition of the polyisocyanate.

The present invention also provides for the use of these coating agentsfor the production of coatings.

The high-molecular polyol component a1) consists essentially ofwater-dilutable, i.e. soluble or dispersible in water, polymerizationresins or polycondensation resins with a molecular weight Mn of over 500possessing hydroxyl groups, or a mixture of several of such resins. Thedilutability in water of these resins is due to the presence ofchemically bonded carboxylate and/or sulphonate groups whose hydrophilicaction is optionally promoted through the simultaneous use of externalemulsifiers. Suitable polymerization resins or condensation resins arein particular polyacrylic resins and optionally urethane-modifiedpolyester resins including alkyd resins.

Polyacrylic resins suitable as component a1) or as part of component a1)are in particular hydroxyfunctional copolymerizates with a hydroxylnumber in the range of from 15 to 200 mg KOH/g and an acid number in therange of from 5 to 250 mg KOH/g having moreover a content of chemicallybonded carboxylate and/or sulphonate groups of in total 8 to 450milliequivalents per 100 g of solid. Here the acid number refers both tothe free, unneutralized acidic groups, in particular carboxyl groups andthe neutralized acidic groups present, in particular carboxylate groups.The copolymerizates generally have a molecular weight Mn of from 500 to50,000, preferably 1000 to 25,000, determined by the method of gelpermeation chromatography using polystyrene as standard.

The copolymerizates concerned are preferably those such as

A 1 to 30, preferably 1 to 10% by weight of acrylic acid and/ormethacrylic acid,

B 0 to 50% by weight of methyl methacrylate,

C 0 to 50% by weight of styrene, wherein the sum of B+C is 10 to 70% byweight,

D 10 to 45% by weight of one or several C₁ -C₈ alkylacrylates,

5 to 45% by weight of one or several monohydroxyfunctionalalkylacrylates or alkyl methacrylates,

F 0 to 15% by weight of other olefinic unsaturated monomers,

wherein the sum of A to F is 100% by weight, wherein moreover 5 to 100%of the polymerized acidic groups present are present in a formneutralized with aliphatic amines or with ammonia, so that the contentof anionic salt-like groups in the copolymerizates corresponds to theabove data.

The unsaturated acids A and optionally F present in polymerized formare, as stated, at least partly neutralized, so that the resultinganionic groups ensure or at least facilitate the solubility ordispersibility in water of the copolymerizates. In the event that onlylow concentrations of salt-like groups are present, the solubility ordispersibility in water of the copolymerizates may be facilitated by theconcomitant use of external emulsifiers. In any case the dilutability inwater of the copolymerizates must be ensured, either as a dispersion oras a colloid-disperse or molecular-disperse "solution".

The monomers B and C may be varied in such a way that the sum of B+C.contains from 10 to 70% by weight of one of the monomers exclusively,wherein methyl methacrylate is preferred; however the use of both methylmethacrylate and styrene together is particularly preferred.

Examples of suitable C₁ -C₈ alkyl acrylates are methyl acrylate, ethylacrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate,isobutyl acrylate, n-hexyl acrylate, n-octyl acrylate and 2-ethylhexylacrylate. Preferred acrylates are n-butyl acrylate, n-hexyl acrylate,2-ethylhexyl acrylate, particularly n-butyl and/or n-hexyl acrylate.

Examples of suitable hydroxyfunctional (meth)acrylates E arehydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate (throughaddition of propylene oxide to a mixture of isomers containing(meth)acrylic acid), 4-hydroxybutyl (meth)acrylate or any mixtures ofthese monomers. 2-hydroxyethyl methacrylate and the aforesaidhydroxypropyl methacrylate isomer mixture are preferred.

The other monomer components F may be substituted styrene derivativessuch as, for example, the isomeric vinyltoluene, α-methylstyrene,propenylbenzene, C₅ -C₁₂ cycloalkyl (meth)acrylate, vinyl esters such asvinyl acetate, vinyl propionate or vinyl versatate and vinylsulphonicacid, wherein the total quantity of polymerisable acids (carboxylic acidA plus optionally the acids listed under F) does not exceed 30% byweight.

For the neutralization, completely or in part, of the polymerized acidicgroups present, aliphatic amines are suitable such as, for example,triethylamine, 2-amino-2-methylpropanol (1), dimethylethanolamine,diethylethanolamine or any other aliphatic amines, preferably with amolecular weight in the range of 31 to 200.

As already indicated above, the term "polycondensation resin" maycomprise in particular (i) polyester resins free of fatty acids andoils, (ii) fatty acid-modified or oil-modified polyester resins,so-called "alkyd resins" and (iii) urethane-modified derivatives of theresins (i) and (ii).

Polycondensation resins suitable as component a1) or as part ofcomponent a1) are in particular those with a molecular weight Mn in therange of over 500 up to 10,000, wherein molecular weights of up to 5000are in this case determined in dioxane and acetone by steam pressureosmometry with the inferior value being taken as correct where valuesdiffer, and wherein molecular weights of over 5000 are determined inacetone by membrane osmometry. The polycondensation resins generallyshow hydroxyl numbers of from 30 to 300, preferably of from 50 to 200 mgKOH/g and acid numbers (according to the definition given above) of from25 to 70, preferably 35 to 55 mg KOH/g. In accordance with thestatements made above, the carboxyl groups incorporated are convertedinto carboxylate groups by neutralization with amines or ammonia in aquantity of from 30 to 200, preferably 50 to 150 milliequivalents per100 g of solid, wherein this may be a partial or complete neutralizationof the incorporated carboxyl groups, however an excess of amine or NH₃may be used even within the limits of the given quantity range.

The preparation of the polyester resin or alkyd resin takes placeaccording to a known method by polycondensation of alcohols andcarboxylic acids such as are defined, for example, in R ompp'sChemielexikon, Volume 1, page 202, Frankh'sche Verlagsbuchhandlung,Stuttgart, 1966, or are described in: D. H. Solomon, The Chemistry ofOrganic Film Formers, pages 75-101, John Wiley & Sons Inc., New York,1967.

Starting materials for preparing polycondensation resins are, forexample

1- to 6- preferably 1- to 4-valent alcohols with molecular weights inthe range 32 to 500 such as ethylene glycol, propylene glycol,butanediol, neopentyl glycol, 2-ethylpropanediol-1,3, hexanediol, etheralcohols such as di- and triethylene glycol, oxyethylated bisphenols;perhydrogenated bisphenols, also trimethylolethane, trimethylolpropane,glycerol, pentaerythritol, dipentaerythritol, mannitol and sorbitol,monovalent chain-breaking alcohols such as methanol, propanol, butanol,cyclohexanol and benzyl alcohol;

polyvalent carboxylic acids or carboxylic anhydrides with a molecularweight in the range of from 100 to 300 such as phthalic acid, phthalicanhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, trimellitic anhydride, pyrromellitic anhydride,maleic anhydride, adipic acid or succinic anhydride;

aromatic or saturated aliphatic monocarboxylic acids such as, forexample, benzoic acid, hexahydrobenzoic acid, butylbenzoic acid, coconutfatty acid or α-ethylhexanoic acid;

olefinic unsaturated fatty acids and derivatives of olefinic unsaturatedfatty acids such as, for example, linseed fatty acid, soybean oil fattyacid, wood oil fatty acid, safflower oil fatty acid, dehydrated castoroil fatty acid, cotton seed oil fatty acid, arachis oil fatty acid ortall oil fatty acid; synthetic, olefinic unsaturated C₁₂ -C₂₂ fattyacids as well as derivatives obtained through conjugation, isomerisationor dimerisation of such unsaturated fatty acids;

the oils corresponding to the aforementioned natural fatty acids, i.e.linseed oil, soya oil, wood oil, safflower oil, dehydrated castor oil,cotton seed oil, arachis oil, tall-oil or even castor oil;

mono- to trifunctional isocyanates with a molecular weight in the range119 to 350 such as, for example, phenyl isocyanate, stearyl isocyanate,cyclohexyl isocyanate, toluylene diisocyanate-2,4 and -2,6,diphenylmethane-4,4'-diisocyanate, naphthylene-1,5-diisocyanate,3,3'-dichloro-4,4'-bisphenylene diisocyanate, hexamethylene diisocyanateand triphenylmethane-4,4'-4"-triisocyanate.

When preparing polyesters free of fatty acids and oils, the monovalentalcohols and in particular polyvalent alcohols given as examples arereacted in a manner known per se with the polybasic acids given asexamples.

The alkyd resins containing fatty or oily acids are prepared in a mannerknown per se from polyols of the kind given as examples and fromdicarboxylic acids or their anhydrides of the kind given as exampleswith the concomitant use of non-drying, half-drying or drying oils ofthe kind given as examples or their transesterification products withpolyvalent alcohols of the kind given as examples. Fatty acids or oilyacids from natural oils, or synthetic fatty acids or fatty acidsobtainable from natural fatty or oily acids by hydrogenation,dehydration or dimerisation may also be used instead of the oils ortheir transesterification products.

The polyols used for the preparation of the alkyd resins are preferablyat least trivalent alcohols such as glycerol or trimethylolpropane.Tetravalent alcohols and alcohols of higher valency, such aspentaerythritol, dipentaerythritol or sorbitol or mixtures of them withthe aforesaid polyols are particularly suitable for preparingwater-dilutable resins, as high hydroxyl numbers of the alkyd resinspromote the dilutability in water. Divalent alcohols such as ethyleneglycol, diethylene glycol, butanediol or neopentyl glycol may be usedconcomitantly.

Acids or acid anhydrides particularly suitable for preparing alkydresins are adipic acid, isophthalic acid, phthalic acid and, mostpreferably, phthalic anhydride.

The preparation of urethane-modified polyester resins takes place in amanner known per se through the use of isocyanates following thepolycondensation reaction.

The required hydroxyl group content is ensured in a manner known per sethrough a suitable selection of the kind and quantitative proportions ofthe initial components within the limits of the disclosure.

The carboxyl groups necessary to attain the dilutability in water may beintroduced, for example, by forming half esters from a previouslyprepared polyester resin containing hydroxyl groups with acid anhydridesof the aforesaid kind. Tetramethylphthalic anhydride is particularlysuitable for this half-ester formation. The introduction of carboxylgroups may also take place, for example, through the use in thepolycondensation reaction of dimethylolpropionic acid, whose freecarboxyl groups generally do not take part in the polycondensationreaction owing to steric hindrance, so that the incorporation of thisacid occurs exclusively through the hydroxyl groups.

The polyol component a2), i.e. the reactive diluent, consists of atleast one water-soluble compound which for the purpose of the isocyanateaddition reaction is at least monofunctional, preferably difunctional totetrafunctional, is not distillable at normal pressure or has a boilingpoint of at least 150° C., with a molecular weight Mn of under 500,preferably under 300.

Monofunctional compounds such as, for example, n-hexanol,n-butoxyethanol, n-octanol or even amides such as, for example,ε-caprolactam are suitable for the purpose of the isocyanate additionreaction. However, the compounds of component a2) are preferablywater-soluble, at least divalent, in particular divalent to tetravalentalcohols with a molecular weight of under 500, in particular under 300,such as, for example, ethylene glycol, propylene glycol, the isomericbutanediols, pentanediols, hexanediols, octanediols; the polyethyleneglycols or polypropylene glycols corresponding to the givenspecifications as regards molecular weight i.e. glycerol,trimethylolpropane, pentaerythritol, sorbitol, mannitol, or theethoxylation or propoxylation products of these high-functionalalcohols, if these products correspond to the given specifications asregards molecular weight.

Any mixtures of the compounds given as examples may of course also beused.

Component a2) is present in the coating agents according to the presentinvention in a quantity of from 5 to 70, preferably 20 to 50% by weight,related to the weight of component a1).

The polyisocyanate component b) may be any organic polyisocyanate withaliphatically, cycloaliphatically, araliphatically and/or aromaticallybonded, free isocyanate groups that are liquid at room temperature. Thepolyisocyanate component b) generally has a viscosity of from 50 to10,000, preferably 50 to 1000 mPa.s at 23° C. Polyisocyanate mixtureswith exclusively aliphatically and/or cycloaliphatically bondedisocyanate groups having an NCO-functionality (average) of between 2.2and 5.0 and a viscosity at 23° C. of from 50 to 500 mPa.s areparticularly preferred.

The so-called "lacquer polyisocyanates" with aromatically or(cyclo)aliphatically bonded isocyanate groups are particularly suitableas component b), with the aforesaid aliphatic isocyanates, as alreadystated, being particularly preferred. For example, "lacquerpolyisocyanates" based on hexamethylene diisocyanate or on1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) and/orbis(isocyanatocyclohexyl)-methane, in particular those based exclusivelyon hexamethylene diisocyanate, are very suitable. "Lacquerpolyisocyanates" based on these diisocyanates are understood to includethe derivatives of these diisocyanates known per se possessing biuretgroups, urethane groups, uretdione groups and/or isocyanurate groupswhich, following their preparation in a known manner, have beenliberated preferably by distillation of excess initial diisocyanateuntil a residue of less than 0.5% by weight remains. Among the preferredaliphatic polyisocyanates to be used according to the present inventionare the hexamethylene diisocyanate-based polyisocyanates fulfilling theaforesaid criteria and possessing biuret groups such as may be obtained,for example, by the methods disclosed in the U.S. Pat. 3,124,605,3,358,010, 3,903,126, 3,903,127 or 3,976,622 and which consist ofmixtures of N,N', N"-tris-(6-isocyanatohexyl)-biuret with lesser amountsof its higher homologues, as well as the cyclic trimerisates ofhexa-methylene diisocyanate fulfilling the aforesaid criteria such asmay be attained according to U.S. Pat. No. 4,324,879 and which consistessentially of N,N',N"-tris-(6-isocyanato-hexyl)-isocyanurate mixed withlesser amounts of its higher homologues. Particularly preferred aremixtures, fulfilling the aforesaid criteria, of hexamethylenediisocyanate-based polyisocyanates possessing uretdione and/orisocyanurate groups, such as arise through catalytic oligomerisation ofhexamethylene diisocyanate in the presence of trialkyl phosphines. Theaforesaid mixtures with a viscosity at 23° C. of from 50 to 500 mPa.sand an NCO-functionality of between 2.2 and 5.0 are particularlypreferred.

Among the likewise suitable but less preferred aromatic polyisocyanatesaccording to the present invention in particular are the "lacquerpolyisocyanates" based on 2,4-diiocyanatotoluene or technical mixturesthereof with 2,6-diisocyanatotoluene, or based on4,4'-diisocyanato-diphenylmethane or mixtures thereof with its isomersand/or higher homologues. Examples of such aromatic lacquerpolyisocyanates are the isocyanates possessing urethane groups such asare obtained by the reaction of excess quantities of2,4-diisocyanatotoluene with polyvalent alcohols such astrimethylolpropane and subsequent removal by distillation of theunreacted excess diioscyanate. Further aromatic lacquer polyisocyanatesare, for example, the trimerisates of the monomeric diisocyanates givenby way of example, i.e. the corresponding isocyanato-isocyanurates,which are likewise liberated preferably by distillation of excessmonomeric diisocyanates subsequent to their preparation.

In principle the use of unmodified polyisocyanates of the kind given byway of example is, of course, also possible provided these are inaccordance with the given specifications as regards viscosity.

The use of hydrophilically modified polyisocyanates as component b) oras part of component b) is in principle possible but in generalunnecessary owing to the emulsifying action of the components a1) anda2). Polyisocyanates can thus be rendered hydrophilic by, for example,reacting one part of the isocyanate groups with monovalent polyetheralcohols possessing ethylene oxide units, for example, the ethoxylationproducts of simple alkanols with 5 to 100 ethylene oxide units permolecule. An ionic modification of the polyisocyanate components by, forexample, reaction with restricted quantities of dimethylolpropionic acidand subsequent neutralization of the resulting reaction product is inprinciple possible but in general unnecessary.

The auxiliary substances and additives usual in lacquer and varnishtechnology may be present in the coating agents according to the presentinvention in addition to the components a1), a2) and b). Examples whichmay be given are pigments, antifoaming agents, levelling agents,dispersants for pigment distribution, desiccants, fillers, catalysts forthe isocyanate addition reaction, antifoaming agents or solubilisingagents not incorporated into the film. In general 20 to 50% water,related to the total weight, and 0 to 40% of inert thinner, related tothe weight of components a1) and b), is present in the ready-to-usecoating agents.

To prepare the ready-to-use coating agent, the polyisocyanate componentb) is emulsified in the aqueous solution or dispersion of component a1),wherein component a2) may be stirred into the system prior to orfollowing the addition of the polyisocyanate component b). Mixing maytake place by ordinary stirring at room temperature. In this connectionthe quantity of polyisocyanate b) is calculated so as to result in anequivalent proportion of isocyanate groups of component b) to groups ofcomponents a1) and a2) capable of reacting with isocyanate groups offrom 0.5:1 to 5:1, preferably 0.8:1 to 2:1. If necessary the requiredfinal viscosity may be adjusted by further addition of solvent and/orwater within the aforesaid limits.

The optionally used auxiliary substances and additives are incorporatedin the system by stirring preferably prior to the addition of thepolyisocyanate component b).

The present invention provides for the first time aqueous polyurethanelacquer systems with reactive solvents i.e. with reactive diluents whichare incorporated into the coatings by film cross-linking. Besides theparticular ecological aspects of these new lacquer systems and thetechnical advantages of a more favourable processing viscosity andbetter flow properties, the person skilled in the art may in additioninfluence the properties of the lacquers as desired through theselection of the reactive diluents. Thus coatings that are brittle perse may be made more elastic by the elasticising action of the reactivediluents. It is known to the lacquer expert that, for example,long-chained diols have an elasticising action.

On the other hand, in a binding agent system with relatively lowcross-linking density harder and more resistant coatings may be createdthrough trifunctional or polyfunctional reactive diluents.

The hardening of the coatings may take place at room temperature orunder normal baking conditions. Moreover the incorporation of thereactive diluents is dependent on the reactivity of the polyisocyanatesand/or the catalysis on one side and on the selected hardeningconditions on the other. Thus volatile reactive diluents are to bepreferred mainly for hardening at room temperature or for a slightlyelevated hardening temperature. At higher baking temperatures and longcross-linking times the use of less volatile reactive diluents isrecommended.

The aqueous binding agent systems according to the present invention aresuitable for the coating of any substrates, in particular for preparingair-drying or heat-drying coatings on wood, concrete, masonry ormetallic substrates.

The following examples refer to data in "%" and "parts" by weight.

EXAMPLE 1

1127.9 parts of propanediol-1,2, 755.9 parts of tri-methylolpropane,746.2 parts of adipic acid and 1828.5 parts of phthalic anhydride areesterified at 230° C. in a nitrogen atmosphere until an acid number of7.9 and a viscosity of 143 sec (measured for a 60% by weight solution indimethylformamide in accordance with DIN 53211) are attained.Esterification is carried out using a column in order to avoid excessiveloss of propanediol. Moreover, the temperature is raised from 140 to230° C. in steps of 10° C./h. The characteristic data given above areattained after a further reaction time of 3.5 hours at 230° C.

309.5 parts of tetratrahydrophthalic anhydride are added to 3309.7 partsof this resin melted at 130° C. The reaction mixture is maintained at130° C. until the resin has an acid number of 39. The viscosity, 60% byweight in dimethyl-formamide measured in accordance with DIN 53211, is182 sec.

The resin obtained is mixed with ε-caprolactam in the proportion of 80parts of resin to 20 parts of ε-caprolactam. The solution obtained isthen dissolved in butoxyethanol to form a 90% by weight solution.Following complete neutralization with N,N-dimethylethanolamine of thecarboxyl groups contained in the resin, water is added so as to producea solution with the following composition:

52.0% by weight of resin

13.0% by weight of ε-caprolactam

2.3% by weight of N,N-dimethylethanolamine

7.2% by weight of n-butoxyethanol

25.5% by weight of water

Viscosity (21.5° C.): 27900 mPa.s

EXAMPLE 2

2960.0 parts of linseed oil, 680.0 parts of pentaerythritol and 250.0parts of trimethylolpropane are heated to 200° C. over a period of onehour in a nitrogen atmosphere. The temperature is then raised to 260° C.over a further hour. The reaction mixture is concentrated at 260° C.until the viscosity of a 70% by weight solution of the concentratedproduct in xylene, measured in accordance with DIN 53211, is 25 sec.

To 2133.0 parts of the concentration product are added 390.6 parts oftrimethylolpropane, 355.7 parts of benzoic acid, 862.9 parts of phthalicanhydride and 213.8 parts of ®Albertol 626C.--a product of HoechstAG--and the mixture is heated to 140° C. in a nitrogen atmosphere.Condensation is effected in a stream of 3 1 of nitrogen per hour, withthe temperature being raised by 10° C. per hour to a final temperatureof 250° C. At 250° C. the mixture is condensed until an acid number of3.4 and a viscosity of 25 sec (measured for a 70% by weight solution indimethylformamide in accordance with DIN 53211) are attained.

3143.3 parts of the condensation product obtained are then reacted at70° C. with 98.1 parts of an isomeric mixture of 65% of2,4-diisocyanatotoluene and 35% of 2,6-diisocyanatotoluene. Afterstirring for 30 minutes the temperature is raised to 120° C. and thereaction maintained at this temperature until a viscosity of 78 sec isattained (50% by weight in dimethylformamide, measured in accordancewith DIN 53211). Other characteristic data shown by the resin are:

NCO-content: 0.2% by weight

acid number: 3.2 mg KOH/g resin

In the final stage, 2723.0 parts of the resin obtained followingurethanisation are reacted at 130° C. with 359.4 parts oftetrahydrophthalic anhydride. The reaction is monitored by measuring theacid number. After stirring for 2.5 hours at 130° C., the resin has thefollowing characteristic data: ##EQU1## The resin obtained is mixed withhexanediol-1,6 in the proportion 70 parts of resin to 30 parts ofhexanediol. The solution obtained is dissolved in butoxyethanol to forma 90% by weight solution; the free carboxyl groups contained in theresin are completely (100%) neutralized with N,N-dimethylethanolamineand then water is added so as to produce a solution with the followingcomposition:

45.5% by weight of resin

19.5% by weight of hexanediol-1,6

3.1% by weight of N,N-dimethylethanolamine

7.2% by weight of n-butoxyethanol

24.7% by weight of water

Viscosity (23° C.): 47500 mPa.s

EXAMPLE 3

699.7 parts of butoxyethanol are placed in a 6 1 stirring apparatusfitted with stirrer, thermometer, reflux condenser and metering pump, ina stream of 3 1 of nitrogen per hour, and heated to 110° C. Maintainingthe temperature at 110° C., a monomer mixture consisting of 167.9 partsof acrylic acid, 828.0 parts of hydroxypropyl methacrylate (additionproduct of 1 mole of propylene oxide to 1 mole of methacrylic acid),80.8 parts of styrene, 466.5 parts of methyl methacrylate, 44.3 parts ofazobisisobutyronitrile and 16.3 parts of dodecanethiol is pumped incontinuously over a 2.5 hour period by means of the metering pump. Thereaction mixture is maintained at 110° C. until the monomers are as faras possible completely incorporated into the copolymer. This ismonitored by determining the residue of a sample of the polymer solutionapplied in a thin layer which then remains for 1 hour at 120° C. in adrying cupboard. During this time the volatile organic compounds escape.The polymer is left behind and the polymer content of the solution isfound by weighing this polymer residue and relating it to the originallyweighed quantity. After further reaction for 4.5 hours, the followingcharacteristic data were measured:

polymer content=78.8% by weight

viscosity of a 40% by weight solution in butoxyethanol in accordancewith DIN 53211=150 sec

acid number=44.4 mg KOH/g polymer

The solution prepared in this manner is then reacted with 15% ofhexanediol-1,6 related to the total mixture. After the hexanediol hasbeen completely dissolved, the solution is neutralized withN,N-dimethylethanolamine to the extent of 60%, related to the acidnumber of the copolymer, and then diluted with water so that the sum ofcopolymer and reactive diluent is approximately 65%. The exactcomposition is given below.

55.6% by weight of copolymer

9.8% by weight of hexanediol-1,6

2.4% by weight of N,N-dimethylethanolamine

14.9% by weight of n-butoxyethanol

17.3% by weight of water

Viscosity (23° C.): 18800 mPa.s

EXAMPLE 4

5.6 parts of castor oil, 609.0 parts of trimethylolpropane, 508.0 partsof pentaerythritol, 492.8 parts of benzoic acid and 1194.7 parts ofphthalic anhydride in a stirring apparatus fitted with distillationbridge, thermometer and gas-inlet tube are heated to 140° C. in a streamof 3 1 of nitrogen per hour. The temperature is then raised to 260° C.over a period of 12 hours (10° C./h) in a stream of 3 1 nitrogen perhour. The condensation is concluded when the viscosity of a 50% byweight solution measured in accordance with DIN 53211 rises again afterinitial falling.

With the polycondensation carried out in this manner, the resin obtainedhas the following characteristic data:

viscosity (50% by weight solution in xylene measured in accordance withDIN 532111)=40 sec

acid number=5.9 mg KOH/g resin

5.0 parts of the resin thus obtained are then reacted with 329.7 partsof tetrahydrophthalic anhydride at 150° C.

After reaction for 2 hours at 150° C. the following characteristic dataare measured:

viscosity (50% by weight solution in xylene measured in accordance withDIN 532111)=93 sec

acid number=43.2 mg KOH/g resin

The resin is mixed with ε-caprolactam in the proportion 70 parts ofresin to 30 parts of reactive diluent, neutralized withN,N-dimethylethanolamine and then diluted with butoxyethanol and water.

Composition:

45.5% by weight of resin

19.5% by weight of ε-caprolactam

2.5% by weight of N,N-dimethylethanolamine

6.5% by weight of n-butoxyethanol

26.0% by weight of water

Tests on transparent lacquer

The following lacquer polyisocyanates are used in the examples ofapplications described subsequently:

Lacquer polyisocyanate 1

Biuret polyisocyanate based on 1,6-diisocyanatohexane with anNCO-content of 22.0% and a viscosity (23° C.) of 10,000 mPa.s.

Lacquer polyisocyanate 2

Lacquer polyisocyanate containing isocyanurate groups based on1,6-diisocyanatohexane with an NCO-content of 21.5% and a viscosity (23°C.) of 3000 mPa.s.

The solutions described in examples 1 to 4 are mixed with lacquerpolyisocyanate 1 or lacquer polyisocyanate 2 as cross-linking agents inquantities such that correspond to an NCO/OH equivalent proportion of1.5: 1. If necessary solubilising agents (acetone or diethylene glycoldimethyl ether) and further water are added subsequently so as to adjustthe mixture to a viscosity for processing of 50 sec, measured in adrainage cup in accordance with DIN 532111.

These transparent varnishes are then applied by means of a dumbbellshaped spreader in a wet film thickness of 180 μm onto glass plates andhardened at 80 or 120° C. for 30 min. Details and test results are shownin Tables 1 and 2.

                                      TABLE 1                                     __________________________________________________________________________    Compositions of transparent lacquers (data on quantities in parts by          weight)                                                                              Aqueous                 Solub-                                         Transparent                                                                          resin      Cross-linking                                                                              ilising                                        lacquer                                                                              solution                                                                            Quantity                                                                           agent   Quantity                                                                           agent Quantity                                                                           Water                               __________________________________________________________________________    1      Example 1                                                                           20   Lacquer poly-                                                                         14.5 Acetone                                                                             4.8  --                                                    isocyanate 1                                                2      Example 2                                                                           "    Lacquer poly-                                                                         23.5 Diglyme.sup.1)                                                                      7.9  8.9                                                   ioscyanate 1                                                3      Example 3                                                                           "    Lacquer poly-                                                                         24.1 --    --   4.9                                                   isocyanate 2                                                4      Example 3                                                                           "    Lacquer poly-                                                                         16.1 Diglyme.sup.1)                                                                      5.4  --                                                    isocyanate 1                                                5      Example 4                                                                           "    Lacquer poly-                                                                         13.7 "     4.6  6.6                                                   isocyanate 1                                                __________________________________________________________________________     .sup.1) Diethylene glycol dimethyl ether                                 

                                      TABLE 2                                     __________________________________________________________________________    Tests on transparent lacquers                                                 Transparent                                                                           Hardening                                                                             Optical effect             Resistance                         lacquer temperature °C.                                                                of film           Hardness to acetone                         __________________________________________________________________________    1       80      transparent, satisfactory flow                                                                  almost nailable                                                                        yes                                1       120     transparent, good flow                                                                          nailable "                                  2       80      transparent, glossy, very good flow                                                             "        "                                  2       120     transparent, glossy, very good flow                                                             "        "                                  3       80      transparent, glossy, very good flow                                                             "        "                                  3       120     transparent, glossy, very good flow                                                             "        "                                  4       80      transparent, glossy, very good flow                                                             "        "                                  4       120     transparent, glossy, very good flow                                                             "        "                                  5       80      transparent, good flow                                                                          "        "                                  5       120     transparent, good flow                                                                          "        "                                  __________________________________________________________________________

We claim:
 1. An aqueous two-component coating composition containing abinder which consists essentially ofa) a polyol component which isdissolved and/or dispersed in water and consists essentially ofa1) atleast one water-dilutable polyacrylic resin or polyester resin having anumber average molecular weight of greater than 500 and containinghydroxyl groups and chemically bonded carboxylate and/or sulphonategroups and a2) 5 to 70% by weight, based on the weight of component a1),of at least one water-soluble reactive diluent that either is notdistillable at normal pressure or has a boiling point of at least 150°C., has a number average molecular weight of less than 300 and has atleast one isocyanate-reactive group, and b) a polyisocyanate componentwhich has a viscosity at 23° C. of 50 to 10,000 mPa.s and is present asan emulsion in the aqueous solution and/or dispersion of polyolcomponent a), provided that when component a1) is a urethane-modifiedpolyester resin, said polyisocyanate component is a polyisocyanate whichhas not been hydrophilically modified,wherein components a) and b) arepresent in amounts which correspond to an equivalent ratio of isocyanategroups of component b) to isocyanate-reactive groups of component a) of0.5:1 to 5:1.
 2. The coating composition of claim 1 wherein componenta2) is selected from polyvalent alcohols having a molecular weight of 62to less than 300 that optionally contain ether groups and/or estergroups.
 3. The coating compositions of claim 1 wherein component a1)consists essentially of a hydroxy-functional polyacrylic resin having ahydroxyl number of 15 to 200 mg KOH/g, an acid number of 5 to 250 mgKOH/g and a content of chemically incorporated carboxylate and/orsulphonate groups of 8 to 450 milliequivalents per 100 g of solids. 4.The coating composition of claim 3 wherein component a2) is selectedfrom polyvalent alcohols having a molecular weight of 62 to less than300 that optionally contain ether groups and/or ester groups.
 5. Aprocess for preparing a coating composition which comprisesi)emulsifying a polyisocyanate component b) having a viscosity at 23° C.of 50 to 10,000 mPa.s and containing at least one organicpolyisocyanate, provided that when component a1) is a urethane-modifiedpolyester resin, said polyisocyanate component is a polyisocyanate whichhas not been hydrophilically modified, in an aqueous solution ordispersion of a polyol component a) which consists essentially ofa1) atleast one water-dilutable polyacrylic resin or polyester resin having anumber average molecular weight of greater than 500 and containinghydroxyl groups and chemically bonded carboxylate and/or sulphonategroups and a2) 5 to 70% by weight, based on the weight of component a1),of at least one water-soluble reactive diluent that either is notdistillable at normal pressure or has a boiling point of at least 150°C., has a number average molecular weight of less than 300 and has atleast one isocyanate-reactive group, wherein components a) and b) arepresent in amounts which correspond to an equivalent ratio of isocyanategroups of component b) to isocyanate-reactive groups of component a) of0.5:1 to 5:1, and ii) incorporating any optional auxiliaries andadditives in component a) before the addition of polyisocyanatecomponent b).